Joseph Doherty
6b3da93151
A browse-committed AB CIP / TwinCAT / FOCAS tag bound with its model's DEFAULT
data type, not the one the device reported. A browsed REAL committed as
`{"tagPath":"Pump_1_Speed","dataType":"DInt"}` — and those three drivers decode
the wire bytes by that field, not by the raw row's OPC UA DataType — so the tag
read four bytes of a float through an integer decoder and published a plausible
wrong number with no error raised anywhere. FOCAS was missed when #536 was filed.
The type is CARRIED, not derived. Reverse-mapping the leaf's driver-agnostic
DriverDataType looks like the smaller fix and is wrong: SInt/Int/DInt/USInt/UInt
all collapse into Int32 on the way out of the driver, so that version would bind
a 16-bit INT as a 32-bit DINT while appearing to fix the REAL. Drivers now state
their own type name on DriverAttributeInfo.NativeDataType, which reaches the
picker as AttributeInfo.AddressFields["dataType"] and the commit mapper from
there. A leaf that states nothing keeps the model default — the pre-#536
behaviour, kept deliberately as the fallback rather than a guess.
Numeric strings are refused before parsing: Enum.TryParse accepts "9" for any
enum and Enum.IsDefined then confirms it, so an unguarded parse would bind a tag
to a type nobody named. A test caught this in the first version of the guard.
--- and the other half, which the fixture was hiding ---
Test Connect on a device with NO authored tags — every AB CIP device at the
moment an operator first presses the button — reported "CIP handshake failed"
against a healthy controller. That was written down as a fixture limitation
("ab_server doesn't implement @raw_cpu_type"). Both halves of that were wrong:
* @raw_cpu_type is not a libplctag special tag at all (only @raw, @tags and
@udt/ are), so it goes out as an ordinary symbolic name that no controller
defines, and the controller's "tag does not exist" IS the successful answer.
* ab_server answered an unresolvable tag path with CIP 0x03 where a Logix
controller answers 0x04 — ErrorBadParam vs ErrorNotFound, which the probe
classifies oppositely. Fixed in vendored patch 0002.
* With the fixture then telling the truth, the real defect surfaced:
AbCipDriverProbe.IsReachableException matched the native C status spellings
("STATUS_NOT_FOUND"), but libplctag.NET throws with the MANAGED enum name
("ErrorNotFound"). Those substrings can never match, so the reachable
classification could not fire on the exception path — which is the path every
no-authored-tags probe takes. This was failing on real hardware too, not just
against the sim. It now recovers the Status and defers to IsReachableStatus,
so there is one classification rather than two that can drift.
Rejected: switching the fallback to @tags. libplctag builds a tag-listing tag
with NO network I/O, so it reports OK against any TCP listener — measured green
against a Mosquitto broker.
Verification: full solution suite green. Falsification runs confirm exactly the
intended tests go red — 9 for the type carry, 3 (the reachable statuses only) for
the probe classification. Live on docker-dev: browse-committed TestString/
Motor_Run/TestSINT now store String/Bool/SInt, alongside last session's
Pump_1_Speed still holding the wrong DInt. TestSINT is the falsifier — its row
DataType is Int32, identical to TestDINT's, so no reverse map could have produced
"SInt".
Known consequence: pre-existing browse-committed tags keep their wrong dataType;
the fix applies to new commits only.
Claude-Session: https://claude.ai/code/session_015p7wGqy3YpZNCpDzTpGMKo
AB CIP integration-test fixture — ab_server (Docker)
libplctag's ab_server — a
MIT-licensed C program that emulates a ControlLogix / CompactLogix CIP
endpoint over EtherNet/IP. Docker is the only supported launch path;
ab_server ships as a source-only tool under libplctag's
src/tools/ab_server/ so the Dockerfile's multi-stage build is the only
reproducible way to get a working binary across developer boxes. A fresh
clone needs Docker Desktop and nothing else.
| File | Purpose |
|---|---|
Dockerfile |
Multi-stage: build from libplctag at pinned tag → copy binary into debian:bookworm-slim runtime image |
docker-compose.yml |
One service per family (controllogix / compactlogix / micro800 / guardlogix); all bind :44818 |
patches/ |
Applied to the libplctag checkout before the build, in filename order — see Local patches |
Local patches
0001 — serve the Symbol Object listing
patches/0001-ab_server-serve-cip-symbol-object-listing.patch teaches ab_server
to answer CIP service 0x55 (Get Instance Attribute List) on class 0x6B, the
Symbol Object listing a client reads through the @tags pseudo-tag to enumerate
a controller's symbol table. Upstream answers unsupported, which is what left
the AbCip controller browse unverifiable (Gitea #468) — the browse binding was
proven alive, but no backend ever returned a tag.
Two things worth knowing before touching it:
- The reply layout is fixed to the attribute set libplctag asks for —
{0x02 symbol type, 0x07 element size, 0x08 array dimensions, 0x01 symbol name}. A request for a different set is refused rather than answered with a differently-shaped reply the client would misparse. - Entries are packed with no padding. The next entry begins on the byte after the last name byte, even on an odd offset. This is not a detail of the fixture: it is what a controller does, and assuming otherwise is exactly the decoder defect the gate found.
Correctness is checked against libplctag's own list_tags_logix client, not
against our decoder — our decoder is the thing under test, so agreeing with it
would prove nothing. list_tags_logix is the reference implementation exercised
against real Logix hardware:
git clone --depth 1 --branch v2.7.0 https://github.com/libplctag/libplctag.git
cd libplctag && cmake -S . -B build -DCMAKE_BUILD_TYPE=Release && cmake --build build --parallel
./build/bin_dist/list_tags_logix 10.100.0.35 1,0 # expect all nine tags, "SUCCESS!"
Partial-transfer paging is exercised the same way by starting ab_server with a
few hundred tags: all of them should come back, with no duplicates and no gaps
at the page boundaries.
0002 — answer "tag does not exist" the way a controller does
patches/0002-ab_server-answer-tag-not-found-with-cip-0x04.patch changes the reply
to an unresolvable tag path from CIP 0x03 (invalid parameter) to CIP 0x04
(IOI could not be deciphered or tag does not exist), which is what a Logix
controller returns. libplctag translates the two very differently — ErrorBadParam
versus ErrorNotFound — and every client that classifies by status code reads the
first as "your request was malformed" and the second as "the controller answered,
that tag isn't there."
The distinction is load-bearing here: the driver's Test Connect probe falls back to a
name no controller defines, so "tag not found" is the successful answer when a
device has no authored tags yet. Before this patch the fixture reported a perfectly
healthy sim as a failed handshake, and — worse — the discrepancy was written down as
a fixture limitation, which hid a real driver defect behind it for as long as it
stood (AbCipDriverProbe.IsReachableException matched the native C spellings, which
the .NET wrapper never produces, so the reachable classification could not fire at
all). AbCip_WithNoAuthoredTags_ReportsTheControllerReachable in
Host.IntegrationTests is the pin, and it needs the fixture rebuilt from this
patch, not merely running.
Bumping LIBPLCTAG_TAG means re-checking both patches against the new tag. It
is a concrete tag rather than the release branch precisely so that this stays
a deliberate act — the branch moves, and the Dockerfile previously called it
"pinned" while tracking it.
Run
From the repo root:
# ControlLogix — widest-coverage profile
docker compose -f tests\Drivers\ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests\Docker\docker-compose.yml --profile controllogix up
# Per-family
docker compose -f tests\...\Docker\docker-compose.yml --profile compactlogix up
docker compose -f tests\...\Docker\docker-compose.yml --profile micro800 up
docker compose -f tests\...\Docker\docker-compose.yml --profile guardlogix up
Detached + stop:
docker compose -f tests\...\Docker\docker-compose.yml --profile controllogix up -d
docker compose -f tests\...\Docker\docker-compose.yml --profile controllogix down
First run builds the image (~3-5 minutes — clones libplctag + compiles
ab_server + its dependencies). Subsequent runs are fast because the
multi-stage build layer-caches the checkout + compile.
Endpoint
- Default:
localhost:44818(EtherNet/IP standard; non-privileged) - Override with
AB_SERVER_ENDPOINT=host:portto point at a real PLC.
Run the integration tests
In a separate shell with a container up:
cd C:\Users\dohertj2\Desktop\lmxopcua
dotnet test tests\Drivers\ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests
AbServerFixture TCP-probes localhost:44818 at collection init +
records a skip reason when unreachable, so tests stay green on a fresh
clone without the container running. Tests use [AbServerFact] /
[AbServerTheory] which check the same probe.
What each family seeds
Tag sets match AbServerProfile.cs exactly — changing seeds in one
place means updating both.
| Family | Seeded tags | Notes |
|---|---|---|
| ControlLogix | TestDINT TestREAL TestBOOL TestSINT TestString TestArray Pump_1_Speed Line1_Count Motor_Run |
Widest-coverage; PR 9 baseline. UDT emulation missing from ab_server. The last three serve the controller-browse gate and are additive — the read/write suites key off the Test* tags. Motor_Run (9), Line1_Count (11) and TestArray (9) have odd-length names on purpose: entries are unpadded, so an odd name puts every following entry on an odd offset, and a decoder that assumes even alignment loses everything behind it |
| CompactLogix | TestDINT TestREAL TestBOOL |
Narrow ConnectionSize cap enforced driver-side; ab_server accepts any size |
| Micro800 | TestDINT TestREAL |
ab_server has no micro800 mode; falls back to controllogix emulation |
| GuardLogix | TestDINT SafetyDINT_S |
ab_server has no safety subsystem; _S suffix triggers driver-side classification only |
Known limitations
- No UDT / CIP Template Object emulation —
ab_servercovers atomic types only. UDT reads + task #194 whole-UDT optimization verify via unit tests with golden byte buffers. The Symbol Object patch above lists symbols, including their types; it does not add Template Object support, so a browsed UDT still cannot be expanded into members here. - Controller-scope listing only — a program-scope listing arrives with a
leading symbolic segment naming the program, and
ab_serverhas no notion of programs.Program:-scoped tags cannot be browsed here. - Family-specific quirks trust driver-side code — ab_server emulates a generic Logix CPU; the ConnectionSize cap, empty-path unconnected mode, and safety-partition write rejection all need lab rigs for wire-level proof.
See docs/drivers/AbServer-Test-Fixture.md
for the full coverage map.
References
- libplctag on GitHub
docs/drivers/AbServer-Test-Fixture.md— coverage mapdocs/v2/dev-environment.md§Docker fixtures